The present invention relates generally to the field of adaptive antenna array processors for use in adaptive antenna array systems that remove undesired signals from the received signal and at the same time maximize the signal-to-noise ratio by forming a beam on the desired signal.
In omnidirectional high-frequency communication systems, undesired interfering signals from various localized sources lying in various directions can be received along with the desired signals. If these signals are powerful enough, they can seriously degrade performance. The effect of these interfering signals can be reduced or negated by employing an adaptive antenna array. An adaptive antenna array utilizes at least two antennas hereafter referred to as antenna elements, with a receiving system. By appropriately weighting and summing the outputs of the signals received by these antenna elements, the interfering signals can in general be reduced or cancelled.
Typically, these prior art adaptive antenna arrays required a large number of samples to be taken before a null could be formed on an interfering signal, and a beam formed on the desired signal. Also, they could not null an interfering signal without also nulling the desired signal unless either the signal contained a reference identifier, or else the direction of the signal was known.
The use of adaptive spatial nulling techniques to remove undesired signals from desired signals has been established for many years in both the radar and communications fields. See for example, Monzingo and Miller, "Introduction to Adaptive Antenna Arrays", John Wiley and Sons, 1981.